Cathode for discharge devices



Jan. 28, 1936. P. w. BLACKBURN 2,029,013

CATHODE FOR DISCHARGE DEVICES Filed March 23, 1933 INVENTOR PM BZAfY/BVfT/V ATTORNEY ?atented Jan. 28, "11936 UNET gTA'EES Philip W. Blackburn, East Orange, N. .l., assignor to Westinghouse Lamp Company, a corporation of Pennsylvania Application March 23, 1933, Serial No. 662,273

14 Claims.

This invention relates to glow discharge devices and relates more particularly to an improved form of electrode for such devices.

In gaseous discharge tubes such for example as glass bulbs, containinga rare gas such as neon, it is the practice to provide a pair of electrodes between which a discharge takes place when a suitable potential is impressed between the electrodes.

Lamps of the above character and particularly neon lamps have found extensive use in the illumination field. Neon lamps have, therefore, reached a commercial status wherein efiiciency of operation and manufacturing cost are important factors. The most costly parts of a discharge lamp are the electrodes. Good results have been obtained with electrodes in the form of a tube having one end closed and so arranged that the discharge is concentrated within the tube.

Tubular electrodes are preferably provided with a coating of a thermionically active material on the inner surface to give a copious supply of electrons. The coatings are applied in the form of oxides and it isnecessary to heat-treat the coating to reduce the oxides and provide the necessary electron emissive material. It is desirable to use strontium or barium with a suitable binder and the heating, in most cases, is performed by high frequency conduction. The electrodes are provided with a support member which is usually in the form of a conductor sealed into a wall of a bulb. It has been found that during the heat treating operation above referred to the heat travels to the press or wall of the bulb and produces cracks with consequent leaks to the detriment of the useful life of the device.

It is an object of the present invention to provide an electrode so constructed as to dissipate heat during the heat treatment and thus prevent the transfer of sufficient heat to the glass to set up detrimental strains and cause cracks.

Another 'object of the invention is to provide a heat radiating electrode of simple construction formed from sheet metal.

Another object of the invention is to provide a tubular electrode formed of a single piece of sheet metal.

Another object of the invention is to provide a method of making electrodes from a tubular body of sheet metal.

Other objects and advantages of the invention will be more clearly understood from the following description together with the accompanying drawing in which Fig. 1 is a side elevational view of a lamp of the neon type having therein electrodes constructed in accordance with the present invention;

Fig. 2 is a longitudinal cross-sectional view of one end of a discharge tube showing the present electrode with a portion broken away;

Fig. 3 is a side view of one of the electrodes partly in section to show an end of a support member;

Fig. 4 is an enlarged view taken on line IV--IV in Fig. 3; and

Fig. 5 shows, diagrammatically, a section of tubing on a mandrel with forming dies in position to shape the heat radiating fins.

Although an electrode made in accordance with the present invention may be used with various types of discharge devices a practical embodiment is shown and described herein as comprising an elongated tube It as for example a neon tube. Devices of this character are provided with electrodes at opposite ends of the tube and, as shown, electrodes ll constructed in accordance with the present invention may be employed.

An electrode H may consist of a tubular body ll of sheet metal, preferably seamless tubing having a wall thickness of .008 of an inch for an electrode of of an inch diameter although this dimension may be varied in proportion to the size of the electrode desired.

In constructing an electrode from a tubular body a portion of the length of the tube at one end is formed by means of suitable dies l2, as shown in Fig. 5, to press portions l2 toward the longitudinal axis of the tube and about a forming mandrel It. The mandrel is of such size that a passage It is formed to receive an end of a support wire [5 which may be inserted with a tight fit so as to secure the electrode to the support. This support wire is of relatively stiflfconductive metal and is usually connected to a section of wire 16 of such character as to make a hermetic seal in a reentrant portion or press ll integral with the wall of the tube Ill. The wire I6 is provided with a conductor I8 which extends from the tube for the passage of electrical energy from a suitable source to the electrode. The conductive support l5, wire l6 and conductor l8 may be considered as a conductive support.

When forming the end of the tube H to provide a recess for the end of a support wire, portions of the metal wall of the tube are compressed to provide vanes or fins l9 which, in the present construction are disposed in radial relation to the axis of the tube. These fins may be disposed in any other relation as for example in planes tangent to the tubular recess M. For the purpose of providing an electrode wherein the glow is concentrated therein, the bottom or closed end of the electrode is provided with what may be termed a conical wall. This wall is of decreasing diameter from the wall of the electrode proper to the wall of the passage M.

It has been found that by making the electrode with an inner end of relatively less crosssectional area than the outer end or mouth, that a more effective and concentrated glow is provided.

It has also been found that by reason of the.

fins IS on the inner end of the electrode that the glow does not occur so readily around this portion of the electrode and is more completely confined to the interior of the electrode.

The present invention provides a decided improvement in electrodes for discharge devices giving a construction which serves to greatly reduce losses through leaks due to an excessive amount of heat reaching the seal.

Although a preferred embodiment of the inven- .body having a reduced tubular portion integral with said fins to receive a support member.

2. An electrode for a glow discharge device comprising a tubular body having a portion of the inner surface coated with a thermionically active material, one end of said body being closed by a support member and vanes extending from said end.

3. An electrode for a glow discharge. device comprising a tubular body having a conical end wall terminating in a tubular extension to receive a support member and vanes extending from said tubular extension.

4. An electrode for a glow discharge device comprising a tubular body having a conical end wall terminating in a tubular extension to receive a support member and fins extending from said comprising a tubular body of sheet metal having tubular extension. v

5. An electrode for a glow discharge device comprising a tubular body having a conical end wall terminating in a tubular extension to receive a support member and a plurality of radial fins disposed in planes intersecting the longitudinal axis of said body.

6. In combination, a glow discharge device having a glass envelope, a conductive lead wire secured in a seal in the wall of said envelope, a tubular metallic electrode supported on said wire in close relation to said seal and vanes integral with said electrode for dissipating heat to prevent excessive heating of said seal.

'7. In a glow discharge device the combination with a glass envelope having a conductive lead wire secured in a seal in the wall of said envelope, a tubular metallic electrode supported on said wire in close relation to said seal, a reduced portion integral with said electrode to receive said Wire and heat radiating fins integral with said reduced portion and parallel to the longitudinal axis of said reduced portion.

8. In a glow discharge device the combination with a vitreous envelope having a conductive lead wire sealed through the wall thereof, a tubular electrode having one end open and the opposite end reduced in diameter to receive an end of said lead wire, heat radiating vanes integral with said reduced portion and disposed between said tubular electrode and said seal to prevent overheating of said seal during the operation of said device.

9. An electrode for a glow discharge device comprising a tubular body of sheet metal having integral longitudinally extending vanes in the form of folds of said sheet.

10. An electrode for a glow discharge device comprising a tubular body of sheet metal having a reduced portion at one end to receive a lead wire and vanes of folded sheet metal extending longitudinally of said reduced portion.

11. An electrode for a glow discharge device comprising a tubular body of sheet metal, one end of said body being closed by a support memher, and vanes formed from said sheet metal extending from said end.

12. An electrode for a glow discharge device comprising a tubular body of sheet metal, one end of said body being reduced to receive a support member, and vanes formed from said sheet and.

- extending from said end.

13. An electrode for a glow discharge device comprising a tubular body of sheet metal having a reduced portion at one end to receive alead wire and vanes extending longitudinally of said reduced portion, each of said vanes having a thickness equal to twice the thickness of said sheet metal.

14. An electrode for a glow discharge device a reduced portion at one end including a cylindrical portion to receive a lead Wire and a conical portion, vanes extending from said reduced portion, each of said vanes including a double thickness of said sheet metal.

PHILIP W. BLACKBURN. 

